In glass production, molten glass is produced in a melting furnace and then passes along a forehearth before being led away for further processing. For example in the production of glass articles the molten glass from the forehearth may pass to a spout where it is formed into gobs which are subsequently formed into the desired articles. Generally in any particular installation there are several forehearths each with a spout fed by a single melting furnace.
Conventional forehearths comprise a refractory trough along which the molten glass flows e.g. to the spout. It is a problem of forehearths that the molten glass at the edge portions tends to cool more rapidly and thus be at a lower temperature than the molten glass in the central part of the forehearth. These differences in temperature of the glass result in different viscosities and accordingly in differences in the speed with which the molten glass moves down the forehearth. The central, hottest glass will be least viscous and thus move down the forehearth faster than the more viscous glass at the edge of the forehearth. This all results in substantial inhomogeneity of the glass across the forehearth. This in turn means that the gobs formed from that glass are not uniform and accordingly leads to variation in the glassware made from those gobs.
It is known to mount gas burners along the edges of a forehearth above the molten glass in the forehearth so that the glass in the edge regions becomes heated to decrease the cooling at the edge portions of the glass and accordingly to make the glass more homogeneous across the forehearth.
In many forehearth installations however the use of gas burners is not appropriate. In some locations gas is not available at all and in other locations, while gas may be available, it is not feasible to use it economically. For example in some countries of the world, hydro-electricity is a relatively cheap power source.
It is known to heat molten glass by means of electrodes submerged in the glass. Current is passed between electrodes, through the glass, to heat the glass, particularly along the edge of the molten glass stream. This improves the homogeneity of the molten glass but results in considerable corrosion of the submerged electrodes.
It is also known to provide radiant heating electrode elements along the length of a forehearth and each of which passes across the forehearth perpendicular to the direction of glass flow and above the level of the molten glass in the forehearth. While this does provide for electric heating of the molten glass in a forehearth while avoiding the problems associated with submerged electrodes, the glass is heated across the whole width of the forehearth and thus use of such an element does little to overcome the problems of inhomogeneity due to temperature differences across the molten glass.